1. Field of the Invention
The present invention relates to a magneto-optical recording and reproducing apparatus to be used in an external memory unit of an electronic computer, a recording and reproducing apparatus of audio, video or other information, and the like.
2. Description of the Prior Art
The magneto-optical recording and reproducing apparatus has been recently enhanced intensively in performance by shortening the recording, reproducing and erasing time of information in a magneto-optical recording medium, increasing the recording capacity, and accelerating the access speed.
In the magneto-optical recording and reproducing apparatus, moreover, there is a growing need for an overwrite function. As an effective method, research is actively concentrated on the magnetic field modulation overwrite method using a bias magnetic field generating apparatus which has a short inverting time in the direction of the magnetic field.
A conventional magneto-optical disk apparatus is explained below by referring to FIG. 6 which is a perspective view of a conventional magneto-optical disk apparatus.
In FIG. 6, numeral 1 is a magneto-optical disk, 2 is an objective lens actuator, 3 is an optical head, 4 is a first drive coil, 5 is a first magnetic yoke, 6 is a first magnet, 7 is a first guide shaft, 8 is a magnetic bias field generator, 9 is a support beam, 10 is a connector, 19 is a spindle motor, and 20 is a base for the mechanism.
This construction is described below. In FIG. 6, the magneto-optical disk 1 possesses a magneto-optical recording layer. The objective lens actuator 2 is fixed on the optical head 3. The optical head 3 is slidably supported by the first guide shaft 7 so as to be free to move linearly in the radial direction of the magneto-optical disk 1. The connector 10 is fixed on the optical head 3. The magnetic bias field generator 8 is positioned by the connector 10 through the support beam 9. Its positioning range is the area in which the optical axis of the light spot emitted to a desired radial position of the magneto-optical recording layer of the magneto-optical disk 1 from the objective lens actuator 2 is located within its effective magnetic field region. The first drive coil 4 is fixed on the optical head 3. The first magnet 6 is fixed on the first magnetic yoke 5, thereby composing a magnetic circuit.
The operation of thus composed magneto-optical disk apparatus is described below. The optical head 3 obtains the driving force by the magnetic field generated by the magnetic circuit composed of the magnetic yoke 5 and magnet 6, and the electromagnetic field generated by the current passed into the drive coil 4 fixed on the optical head 3. Further, to meet the request of the magnetic field modulation overwrite mentioned above while maintaining a high density recording, it is necessary to shorten the magnetic field inverting time of the magnetic bias field generator 8. For example, a same capacity as the magnetic head used in a magnetic recording apparatus (such as hard disk apparatus) is required. The effective magnetic field region of such a magnetic bias field generator 8 (the distance to the medium, the region on the medium) is characterized by narrowing in correlation with the shortening of the magnetic field inverting time. Accordingly, the connector 10 is mechanically responsible for proximity positioning of the magnetic bias field generator 8 and magneto-optical disk 1, and positioning for matching the optical axis of the light spot from the optical head to the vicinity of the center of its magnetic field region. Furthermore, while the optical head 3 is moving in the radial direction of the magneto-optical disk 1 (at the time of track access), the connector 10 is moving the both in phase while maintaining the mutual relative positions.
In such a conventional structure, however, the following problems were experienced because the magnetic bias field generator and the optical head are mechanically coupled by means of an elastic support member and connector.
First of all, there is a problem of volumetric change of the mechanical coupling part due to temperature changes in the apparatus during operation of the apparatus. In other words, an error is caused in the relative positions due to volumetric changes of the mechanical coupling part, between the gap position of the magnetic bias field generator and the light spot position of the optical head, which should be on the same track position of the magneto-optical medium.
Next, a positioning error occurs between the magnetic bias field generator and the optical head when assembling the apparatus. That is, the positional error between the two among individual apparatuses may lead to deterioration of reproducibility of the recording, reproducing and erasing actions in the same conditions on a certain variable magneto-optical disk.
Another problem is the disturbance by the magnetic bias field generator to the track access characteristics due to the optical head. The magnetic bias field generator oscillates while following up the surface deflection of the magneto-optical disk. This oscillating action is transmitted to the optical head through the connector, and becomes a disturbance to lead to resonance of the pitching mode of the optical head.
Therefore, the mechanical coupling of the optical head and the magnetic bias field generator may induce relative position deviations of the magnetic bias field generator and optical head due to assembling error or temperature characteristics, or deterioration of dynamic characteristics of the optical head due to transmission of vibration energy.